This invention relates to a fuel spacer for fuel assemblies in nuclear reactors, and more particularly to an independent cell type fuel spacer for fuel assemblies mentioned above.
A fuel spacer is used to arrange a plurality of fuel rods, which constitute a fuel assembly, while leaving therebetween gaps of a predetermined size, which are utilized as passages for a coolant.
Some spacers have been changed from a general type spacer of a lattice structure to a circular or regular octagonal independent cell type spacer disclosed in Japanese Patent Laid-Open No. 87384/1979 (basic application: Swedish Application No. 7714562-1 filed on Dec. 21, 1977); in a general type spacer, a pressure loss which occurs due to resistance to the water flow is occasionally a cause of flow instability and, in an independent cell type spacer, a pressure loss can be reduced to an advantageously low level.
It is necessary that a plurality of fuel spacers be arranged at predetermined intervals in the axial direction of a fuel assembly. In order to support these fuel spacers, spacer support rods are used.
It is necessary that at least one spacer support rod be provided in the central portion of a fuel assembly. A fuel rod was sometimes utilized as a spacer support rod. In such a fuel assembly, the fission rate of the fuel in the central portion thereof is low. In order to make uniform the fission rate of fuel in a fuel assembly, a spacer support rod consisting of a hollow water rod, through which the water can be passed, is used at present.